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EESA06H3 Final: EESA06 Final Notes (Chapter 8-10)

Environmental Science
Course Code
Nick Eyles
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EESA06 Finals Notes
Lecture 8
deep time/ geologic time- 4.5 billion years ago
In the last 20 years that we’ve developed relatively inexpensive methods that can be
readily duplicated around the world for age dating rocks.
absolute age= real age
Relative age dating - Well based on mapping in the field, mapping of rock layers, this rock
layer is older than this other rock layer.” Strata- layers of rock
Stratigraphy- the sub-discipline of geology which is concerned with age of rocks.
- study of how all those rocks are arranged in time as revealed by strata.
Accommodation- in order to get rocks preserved, areas of the crust must subside (Ocean
basins, subduction zones, other types of basins) that way it usually floods with water and
accumulate sediment.
Basins- the crust to be sinking over broad areas or subsidence.
Uplift- opposite of subsidence, results in non-accommodationà erosion and removal of
sediment and rock, tectonics
Ex: Grand Canyon area must subside in the past in order to accommodate its layers.
- Bottom= Oldest layer
- Top= youngest layers
succession- is where those layers sit on each other without any major breaks. It’s almost like a
continuous record of environments
unconformable succession where there are major time breaks within the succession.
“More gaps than record”- last 4.5 billion years of earth history there’s more time which is
unrecorded by rocks than there is that is actually recorded. Rock record is incomplete. That there
are major gaps. Because a lot of rocks, a lot of sediments record distinct events separated by long
periods where nothing happens.
Fossil - fossilized, lithified remains of an organism. Organisms evolve through time. So if
we look at any one fossil type and compare that with other types elsewhere, we can usually
put them in some sort of relative age position.

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formal succession- the succession of fossil types that record evolution through time. “Well
this fossil has more primitive characteristics than this one, so it’s older.”
Index fossils- organisms that evolved very quickly
Grand Canyon
- Everything is flat line. That’s not the case in many parts of the world where the rocks
have been broken.
- rocks get broken by fault à a lot of energy or Earthquakes.
brittle failure- Rocks will break
- processes usually happen at fairly shallow depths in the earth’s crust. Fairly shallow
depths where rocks are cold.
Plastic deformation- Deeper, when rocks are warmed up and bend and fold
Complex folding and deformation (faulting, folding) at some places in the world, the youngest
rocks can be at the bottom and the oldest rocks have been pushed over them
Isotopes- chemical species that are unstable and produce daughter products.
- used in the steady decay of unstable isotopes to know the absolute age isotope dating
or radiometric dating- the rate at which isotopes break down is known. It’s at a steady
constant rate. Using laboratory methods, we can determine the ratios between the amount of
parent isotope and daughter product in a rock which gives the absolute age.
Uranium 238- it’s unstable and breaks down by radioactive decay and the
end daughter product is lead, Pb, lead.
- Measure the amount of uranium 238 in lead in a sample. Look at the ratio between the
two amounts and that gives us some idea of age.
half-life= rate of decay
- different with different isotopes
- the amount it takes for half of the parent isotope to be turned into lead.
- Some break down very quickly. They have half-lives of hours or days. Other isotopes
have half-lives of millions of years.

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Unconformity- So the layers on top are sitting uncomfortably on the rocks
Older layers in the strata are not flat. It’s been tilted by tectonic processes.
Dip= tilt
Plutons- The bodies of igneous rocks which have come up from depth and intruded younger
rocks. Granite pluton that’s intruded in. It’s been intruded as a molten magma.
- Then this layer was depositedàThompson River formation. Sedimentary basins-
substance of the earth’s crust which allows deposition of sediment over broad areas.
Geologists name layers after the local place. So there is a place called
Revelstoke, Kamloops in British Columbia
Formation- refers to a distinct strata. Example, Revelstoke formation
- have distinctive fossils or structures in it. It may have
distinctive unconformable succession, but even in there, there are slight breaks. And
these are called disconformities not unconformities
- unconformity is where someone has ripped out three chapters out of your book.
- disconformity is where someone has ripped out a page.
- Disconformity generalizes a mini unconformity.
The disconformities is more than what is recorded in the rock. More gaps than record.
Index fossil- used to correlate it across large areas.
Ex: Canyon and Australia, they’re separated by oceans today but during Pangea or Rodina,
those places were quite close. Using index fossils, gaps are recognized. Index fossils are
missing. Volcanic ash and a lot of volcanic eruption short lived.
Ash layers- give a high-resolution correlation from one area to another. Thus, it can
be dated. Then, you can match rocks elsewhere based on the presence of volcanic ash
arising since the deposition of ash is virtually instantaneous.
Example: A type of fossil lived over many millions of years. We find it in all layers. It
wouldn’t be any use as an index fossil because it’s common. We want those types of
fossils that are actually rare because they only record very short instances of time.
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